Didelta spinosa, the great salad thistle or in Afrikaans the perdeblom (horse flower) and locally in Namaqualand the t'arda from the times of Khoi or San languages, is a shrub from 1 m to 2 m in height.
A small patch of still unopened disc florets can be seen in the centre of the disc of the flowerhead in picture. Some withered disc florets on the outside of the disc right next to the rays and a ring of currently flowering, unkempt pale yellow disc florets inside them, indicate how the opening begins on the outside and gradually reaches the florets closer to the centre. On each ray floret two longitudinal grooves are present, as well as notched tips on some of them. The photo was taken near Springbok early in September.
The species is distributed in a broad coastal strip in the Northern Cape and the northwest of the Western Cape, from Saldanha to the Gariep. It also grows in Namibia and is well-known in Namaqualand.
This plant's habitat is dry sandy and rocky, sometimes granite slopes and flats, often the greenest entity among the greyish scrub. The species is not considered to be threatened in its habitat early in the twenty first century (Manning, 2009; http://redlist.sanbi.org).